I've used enviromesh for 3 years and have been free of carrot fly.
Prior to using it growing carrots was a waste of time.
I use the mesh over a cloche.

Carrot fly do not fly higher than 2' off the ground so plant in pots if you can. I don't get carot fly using that method. My brother used environmesh with good results. He planted in the earth. He used it as a fence round his carrot plot rather than over the carrots so he could weed them etc.

Planting 2 foot off the ground doesn't work unless you can guarantee that whatever they are on is that tall all round.
I thought i would be safe last year planting in a container 15" deep on a wall 15" above ground level. Trouble was the back of the wall was level with the fence so the fly's managed to get in.